Impedance Matching Networks (PRODIK-Series)
Application
The RF impedance matching networks of the PRODIK-Series automatically match the impedance of a plasma to meet the requirements of a power supply with an operating frequency of 13.56 MHz. Different circuits are able to match diodes, magnetron cathodes and big planar electrodes for PECVD and etching with low loss of power.
The networks (matchboxes) are optimized for highest stability of plasma processes and they provide leading measuring techniques and automatic control. This results in an optimal user friendliness and best process control.
Hardware
In manufacturing our matching networks we make no compromises concerning quality and reliability. High class ceramic and vacuum capacitors as well as silver-plated conductive parts at highly loaded locations guarantee a high operating reliability and reproducibility. The casing boxes are made of aluminum and all covers have copper-beryllium spring contact strips. This utilizes a high-grade RF radiation shielding which also allows the usage of just a few quick acting closures to remove the covers.
Measuring Techniques
Via capacitive voltage dividers, two voltages are measured at a fixed capacitor at the input of the matchbox. These voltage dividers are designed to be low-coupling; thus, crosstalk is being suppressed.
Currents are calculated from the voltage differences; direct current measurements with inductive couplers, which are susceptible to errors, are eliminated.
The detected values are registered by a logarithmic amplifier. This technology permits very high precision at a maximum of companding.
The measured data is used to calculate input impedance and, with reduced precision, load impedance. From these figures, the controller determines the ideal set-up of the variable capacitors. Input and load impedance can be indicated or processed further via system control.
Furthermore the DC bias potential is measured at the output of the matchbox and a plasma detector recognizes whether the plasma has ignited or not.
Control Concept
The PRODIK-Series convinces with innovative sensor technology and modern CAN-Bus technology with local intelligence.
All measuring signals are A/D-converted immediately after their registration and then transferred digitally - thus loss-free and stable against electromagnetic interference - via the bus.
The motor drives of the vacuum capacitors are also equipped with their own set of electronics (CUB) including motor drivers, position registration and the CAN interface. Communication with the central controller uses direct pF gauging. Thus, a complete, pre-adjusted capacitor unit, including the driving mechanism, can be replaced without requiring any line-up activities. All process parameters are directly reproducible.
The central controller, ASC, has a standard equipment consisting of the CAN-Bus, an RS 232 interface and a Profibus.
A universal analog/digital interface card (GCT) is available for the integration of an RF generator. Via this card, the ASC can assume complete control of the RF generator, thus permitting to drive the entire RF system including a non-profibus-compatible generator via the Profibus interface of the ASC.
As already mentioned, for autotuning, 2 voltages are measured at the fixed capacitor at the input. This figure is then used to calculate the input impedance, which then, with reduced precision, establishes output or load impedance. As an option the output impedance can be directly detected and then used to regulate the power exactly.
By means of the load impedance, it is possible to determine the reactive power, the output current and other process relevant parameters.
Those can be checked and indicated by the ETHOS configuration software or processed further via the control system.
Furthermore the output current can be limited in order to save the equipment.
Complete modularization permits quick and flexible, purely software supported adaptation of the control concept to all kinds of different demands. For example, software variants are available for quick cycle time operations with sputtering times of merely seconds. Here, classical autotuning would not be applicable.
AURION's technology permits a combination of a stable short sputtering process with automatic compensation of the drift between the processes, thus ensuring all advantages.
